Plasma arc systems can be used for a variety of cutting or welding applications. Typically, plasma arc systems apply an electric current through an ionized gas or plasma to form a plasma arc. The plasma is sufficiently hot to melt the workpiece in order to cut or weld the workpiece.
Plasma arc systems can require significant amounts of power to generate and sustain the plasma arc. Various power supplies for supplying power to plasma arc systems exist. These power supplies typically receive a high voltage AC input from a mains supply or other power source and provide the high power output necessary to support the plasma arc.
One type of power supply for a plasma arc system is a buck converter or chopper type plasma power supply. Chopper plasma power supplies can be used to provide a high DC output current, such as about 10 amperes to about 400 amperes, that is used by the plasma arc system to generate the plasma. Chopper type plasma power supplies consist of a large 50/60 Hz isolation transformer followed by one or more choppers connected in parallel.
For instance, FIG. 1 depicts a conceptual diagram of an exemplary conventional chopper plasma power supply 10. Power supply 10 includes a large isolation transformer 12 followed by a plurality of chopper circuits IC1, IC2, . . . ICn connected in parallel. Each chopper circuit IC1, IC2, . . . ICn includes a rectifier 22 for converting the AC output of isolation transformer 12 to a DC signal for a DC bus 24. A chopper 26 converts the DC signal from DC bus 24 utilizing known pulse width modulation (PWM) techniques to generate a unipolar pulse signal having a high frequency, such as about 10 kHz to about 25 kHz. An inductor 28 filters the pulse signal provided by chopper 26 to produce DC outputs I2, I2, . . . In. The DC outputs I2, . . . In of each of the chopper circuits IC1, IC2, . . . ICn are combined to provide the desired DC output current IDC OUTPUT for the power supply.
To accommodate the various AC power supply inputs available throughout the world, a chopper supply typically must utilize a large front end isolation transformer having multiple taps or the chopper supply must utilize multiple transformers to accommodate different voltages, leading to increased inventory and costs.
Power supplies that include converter circuits to avoid the need for large front end isolation transformers exist. For instance, U.S. Pat. No. 6,849,827 discloses a method and apparatus for receiving a universal input voltage in a welding power source. However, these power supplies can be limited in output DC current rating. To increase the output current rating of such power supplies, higher rated power devices, such as higher rated fast recovery diodes, IGBTs and high frequency magnetics, typically must be used in the converter circuits, leading to increased costs. Moreover, these components may be limited in their current and or switching characteristics limiting their use to the lower output currents required for plasma systems. This prevents these types of converters from being used to provide high output currents from a wide range of AC power source inputs as desired.
Thus, a need exists for a universal power supply that is capable of efficiently providing a wide range of high DC output currents from a wide range of AC power supply inputs that overcomes the above mentioned disadvantages.